Benthic biodiversity and bottom-up effects based on foodweb attributes in response to sediment condition in Sado estuary (SW Coast, Portugal)

Abstract

Studies that concurrently assess diversity patterns and interactions among benthic organisms remain scarce. This research aims to investigate how benthic community diversity influences trophic interactions and the structure of benthic food webs, providing fundamental knowledge to support the development of new approaches for assessing Descriptors 1, 4 and 6 (Marine Strategy Framework Directive). Spatial-temporal patterns of benthic bacterial and nematode communities in response to sediment conditions were analysed at three sampling sites in Sado estuary (Portugal) using 16S metagenomic and morphological identification, respectively. Both communities exhibited comparable responses to environmental variables, although nematodes were more sensitive to site-specific variations than bacteria. The co-occurrence of specific taxa suggests potential interactions these communities most likely influenced by local anthropogenic activities, emphasizing their value as effective ecological indicators. Benthic food webs were analyzed through stable isotope ratios δ13C and δ15N of macrobenthic organisms and their potential food sources. Isotopic metrics were combined with multivariate methods to identify food web indicators. Trophic structure, aligned with the benthic diversity, revealed a clear spatial pattern driven by sediment grain size, organic matter content, and primary production. “Navigator” and “Gambia” sites exhibited simpler food webs, consistent with organic enrichment, dominance of anaerobic bacteria, and prevalence of opportunistic nematode genera. Temporal variability of both food webs was driven by differences in the resources. In contrast, “Tróia” food webs were more complex, with a high diversity of consumers and efficient resource exploitation. Overall, spatial differences were more pronounced than temporal trends, although food web complexity increased over time at 'Navigator' and 'Gambia'. The 'Tróia' food web exhibited only minor temporal variation, reflecting subtle changes in resource use. This study introduces a novel approach integrating benthic diversity and trophic interactions to assess estuarine habitat condition, supporting Blue Economy activities, habitat recovery, and sustainable coastal management.